The French Army sent paratroopers into the battle zone of the Chadian civil war, where they could face Libyan-backed Chadian dissidents in renewed ground fighting. France announced that developments on the battlefield would determine whether additional troops--beyond the 500 already committed to Chad--would be sent here.

The French shift of about 200 paratroopers to the strategic eastern town of Abeche, coupled with the possibility of sending more soldiers, marked a move away from President Francois Mitterrand's two-year avoidance of military intervention in African ex-colonies. Such involvement, which Mitterrand's socialist government had branded "neocolonial," was common under previous French governments.

Col. Bernard Messana, commander of French forces in Chad, told reporters that a "reinforced company" of paratroopers was moving to Abeche to instruct government soldiers in the town's defense. "They will not attack unless they are attacked" by the Libyans or Chadian rebel forces, Messana added.

The French shift came amid reports of stepped-up Libyan bombing attacks on government positions in northern Chad, interpreted as a prelude to ground attacks pointed at the capital here.

President Hissene Habre's embattled government appealed to France and the United States yesterday for "direct, massive and urgent" military intervention. In Paris today, Foreign Minister Claude Cheysson said French aid to Chad would develop "according to the circumstances." France has said the forces are for training purposes only.

President Reagan said this week that there would be no direct U.S. military intervention in Chad. The United States has a strategic interest in what happens here because of the proximity to Egypt and Sudan. Those two close allies are under consideration for base sites of the U.S. Rapid Deployment Force.

Both France and the United States have sent the government tons of logistical equipment, arms, rockets and antiaircraft missiles. But the French and U.S. supplies are no match for Libya's arsenal of Soviet-supplied arms, which includes thousands of tanks and hundreds of combat aircraft.

An informed source said today that Libyan supplies continue to flow into the rebel-held northern town of Faya Largeau, which fell to the dissidents and a Libyan armored column on Wednesday.

In other developments, the government-evacuated town of Koro Toro was occupied today by the rebel forces, informed sources said. Koro Toro is on one of two main routes leading to Ndjamena.

Information Minister Mahamat Soumaila said Libyan planes bombed the towns of Oum Chalouba and Kalait for the third day. Other sources said Habre's forces had pulled back to a crossroads at Arada, halfway between Oum Chalouba and the town of Biltine.

The major part of the government troops who retreated from Faya Largeau on Wednesday are in the town of Salal, south of Koro Toro, Soumaila said. This route leads to the capital through western Chad.

The bombing of Oum Chalouba is seen as preparation for a military drive to Abeche, 400 miles east of Ndjamena. Abeche sits on Chad's east-west highway to the capital.

The French commander said three Puma military helicopters will also be sent for use by French troops at Abeche. The helicopters were to arrive in Ndjamena today during an all-day shuttle of French cargo planes that also brought more of the 500-man paratrooper force.

Abeche, Chad's second largest city, is near the Sudan border. It was from Abeche that Habre made his drive across Chad and captured Ndjamena in June last year from then-president Goukouni Oueddei's coalition forces. Goukouni now leads the insurgents.

Habre and his guerrillas at one point were forced to flee into Sudan, closely pursued by a Libyan force that had entered the civil conflict at Goukouni's invitation. It was after Goukouni asked the Libyan force to withdraw, at the end of 1981, that Habre was able to take Ndjamena and force Goukouni to flee.

Goukouni is now reported to be sharing power with two new faces in the Chadian power game: Gen. Negue Djogo, 51, a former French Army soldier who fought in Vietnam and Algeria, and Acheikh Ibn Oumar, 32, a supporter of Libyan leader Muammar Qaddafi.

Today, Habre's government put on display 13 bedraggled prisoners of war who Information Minister Soumaila said were Libyans captured at Faya Largeau when government forces had retaken the town on July 30. After Habre's forces retreated from Faya Largeau on Wednesday the prisoners were transferred to Ndjamena, officials said.

Reporters were not allowed to talk to the prisoners, who stood on a stage in downtown Ndjamena's Chamber of Commerce building. One was emaciated and suffering from a hip wound.

In the evening, reporters were allowed into Ndjamena's central prison to view 160 prisoners who Soumaila said were "Sudanese mercenaries" also captured at Faya Largeau. This second group allegedly was from Qaddafi's Islamic Legion, a fighting force described by critics as made up of Africans press-ganged into service after they arrived in Libya looking for work. Several said in English they were from Sudan.